Preparation and some properties of stable and carbon-14 and tritium-labeled short-chain aliphatic hydroxamic acids

A simple and safe procedure has been described for the preparation of short-chain aliphatic hydroxamic acids in quantities as large as 1 mole and as small as 0.01 mole. The procedure is equally suitable for the preparation of isotopically labeled hydroxamates, as has been demonstrated in the case of 1-¹⁴C-acetohydroxamic acid and ³H-acetohydroxamic acid. Some physical and chemical characteristics, including infrared spectra of formo-, aceto-, propiono-, and isobutyro-hydroxamic acids prepared by this method have been described.     

The Aerogenic Response of Escherichia coli and Strains of Aerobacter in EC Broth and Selected Sugar Broths at Elevated Temperatures

Gas formation by 116 strains of Escherichia coli and 104 strains of Aerobacter was determined in a specially constructed and accurately controlled water bath employing EC, lactose, maltose, sucrose, glucose, levulose, and galactose broths at temperatures ranging from 44.5 to 46.5 C.

Greatest gas activity occurred in EC broth. In the range 44.9 to 45.5 C over 92% of the E. coli cultures formed gas, but the Aerobacter strains dropped from 68 to 2%. A natural point of separation of the two groups occurred at 45.5 C.

Inhibition of the gas-forming mechanism rather than death is the universal response of the Escherichia organisms to these temperatures. The inhibition increases with rising temperatures and is readily reversible. At 46.5 C, 64.5% of all the Escherichia cultures were inhibited and 69.1% of all the cultures were actually viable.

In EC broth it was found that as a group atypical E. coli (-+--) were the most resistant gas-positive types. Least resistant in EC broth was a group of known typical fecal isolates of E. coli (++--). Of intermediate resistance between the two groups was the large body of typical E. coli (++--) organisms.

Certain individual strains of E. coli excelled in the production of gas in the variety of sugar broths tested at elevated temperatures. The Aerobacter strains did not exhibit this property.

Finally it is suggested that elevated temperature incubation studies of this type be conducted in critically controlled water baths with an ascertained accuracy in the vicinity of 45.5 ± 0.1 C under full load.

     

Urease catalysis and structure: X. Alternate bonding-site isozymes of jackbean urease

Three previously uncharacterized, nongenetic urease isozymes have been analyzed by sucrose density gradient sedimentation, gel electrophoresis, and chemical reactivity. The full complement of isozymes could be reliably generated by choosing appropriate levels of NaCl, pH, and ethylene glycol, and was stable for several days in dilute solution. The three forms of interest were found to be quaternary isomers of other isozymes, but differed from them qualitatively in their bonding sites, with disulfide bonds being substituted for noncovalent bonds. The separation of these isomer-pairs during sedimentation and electrophoresis cannot be readily explained by differences in size or charge, but must rather arise from a difference in shape. A simple two-dimensional model can provide the appropriate molecular architecture to satisfy these requirements: Only one of the two half-units in each α-urease molecule undergoes disulfide bonding during polymerization, and it does so with two adjacent molecules, thus producing asymmetric polymers from symmetric starting components.     

The anomeric form of D-fructose 1,6-bisphosphate used as substrate in the muscle and yeast aldolase reactions.

From a series of rapid quench kinetic experiments, it has been demonstrated that muscle D-fructose bisphosphate aldolase catalyzes the cleavage of beta-D-fructose 1,6-bisphosphate but not that of the alpha anomer, although the alpha anomer may be tightly bound. Yeast D-fructose bisphosphate aldolase appears to utilize both alpha and beta anomers of the substrate, with yeast apoaldolase catalyzing the interconversion of the alpha and beta forms.     

Studies on histoplasmosis IV. Elution characteristics of the Histo-inhibitory factor (HIF)

Summary The histo-inhibitory factor (HIF) derived from homogenates of liver or kidney from hamsters infected withHistoplasma capsulatum has been fractionated by column chromatography. It shows maximum absorption at 280 mµ, has a molecular weight of 142,000 and can be eluted from DEAE-cellulose or DEAE-Sephadex A—50 with 0.02 M phosphate — 4 M sodium chloride (1 : 1)HIF can be eluted fromHistoplasma yeast cells at pH 10.0, thus a greater number of positive cultures from chronic histoplasmosis could be expected to result from pretreatment of clinical specimens in glycine buffer pH 10.0 prior to culture.     

Proteomic signatures of in vivo muscle oxidative capacity in healthy adults

Adequate support of energy for biological activities and during fluctuation of energetic demand is crucial for healthy aging; however, mechanisms for energy decline as well as compensatory mechanisms that counteract such decline remain unclear. We conducted a discovery proteomic study of skeletal muscle in 57 healthy adults (22 women and 35 men; aged 23–87 years) to identify proteins overrepresented and underrepresented with better muscle oxidative capacity, a robust measure of in vivo mitochondrial function, independent of age, sex, and physical activity. Muscle oxidative capacity was assessed by ³¹P magnetic resonance spectroscopy postexercise phosphocreatine (PCr) recovery time (τ_PCr) in the vastus lateralis muscle, with smaller τ_PCr values reflecting better oxidative capacity. Of the 4,300 proteins quantified by LC‐MS in muscle biopsies, 253 were significantly overrepresented with better muscle oxidative capacity. Enrichment analysis revealed three major protein clusters: (a) proteins involved in key energetic mitochondrial functions especially complex I of the electron transport chain, tricarboxylic acid (TCA) cycle, fatty acid oxidation, and mitochondrial ABC transporters; (b) spliceosome proteins that regulate mRNA alternative splicing machinery, and (c) proteins involved in translation within mitochondria. Our findings suggest that alternative splicing and mechanisms that modulate mitochondrial protein synthesis are central features of the molecular mechanisms aimed at maintaining mitochondrial function in the face of impairment. Whether these mechanisms are compensatory attempt to counteract the effect of aging on mitochondrial function should be further tested in longitudinal studies.     

Contrasted histories of organelle and nuclear genomes underlying physiological diversification in a grass species

C₄ photosynthesis evolved multiple times independently in angiosperms, but most origins are relatively old so that the early events linked to photosynthetic diversification are blurred. The grass Alloteropsis semialata is an exception, as this species encompasses C₄ and non-C₄ populations. Using phylogenomics and population genomics, we infer the history of dispersal and secondary gene flow before, during and after photosynthetic divergence in A. semialata. We further analyse the genome composition of individuals with varied ploidy levels to establish the origins of polyploids in this species. Detailed organelle phylogenies indicate limited seed dispersal within the mountainous region of origin and the emergence of a C₄ lineage after dispersal to warmer areas of lower elevation. Nuclear genome analyses highlight repeated secondary gene flow. In particular, the nuclear genome associated with the C₄ phenotype was swept into a distantly related maternal lineage probably via unidirectional pollen flow. Multiple intraspecific allopolyploidy events mediated additional secondary genetic exchanges between photosynthetic types. Overall, our results show that limited dispersal and isolation allowed lineage divergence, with photosynthetic innovation happening after migration to new environments, and pollen-mediated gene flow led to the rapid spread of the derived C₄ physiology away from its region of origin.     

Analogs of iso-azepinomycin as potential transition-state analog inhibitors of guanase: Synthesis,biochemical screening,and structure–activity correlations of various selectively substituted imidazo[4,5-e][1,4]diazepines

Guanase is an important enzyme of the purine salvage pathway of nucleic acid metabolism and its inhibition has beneficial implications in viral, bacterial, and cancer therapy. The work described herein is based on a hypothesis that azepinomycin, a heterocyclic natural product and a purported transition state analog inhibitor of guanase, does not represent the true transition state of the enzyme-catalyzed reaction as closely as does iso-azepinomycin, wherein the 6-hydroxy group of azepinomycin has been translocated to the 5-position. Based on this hypothesis, and assuming that iso-azepinomycin would bind to guanase at the same active site as azepinomycin, several analogs of iso-azepinomycin were designed and successfully synthesized in order to gain a preliminary understanding of the hydrophobic and hydrophilic sites surrounding the guanase binding site of the ligand. Specifically, the analogs were designed to explore the hydrophobic pockets, if any, in the vicinity of N1, N3, and N4 nitrogen atoms as well as O⁵ oxygen atom of iso-azepinomycin. Biochemical inhibition studies of these analogs were performed using a mammalian guanase. Our results indicate that (1) increasing the hydrophobicity near O⁵ results in a negative effect, (2) translocating the hydrophobicity from N3 to N1 also results in decreased inhibition, (3) increasing the hydrophobicity near N3 or N4 produces significant enhancement of inhibition, (4) increasing the hydrophobicity at either N3 or N4 with a simultaneous increase in hydrophobicity at O⁵ considerably diminishes any gain in inhibition made by solely enhancing hydrophobicity at N3 or N4, and (5) finally, increasing the hydrophilic character near N3 has also a deleterious effect on inhibition. The most potent compound in the series has a K_i value of 8.0 ± 1.5 μM against rabbit liver guanase.     

Polyploidy does not control all: Lineage‐specific average chromosome length constrains genome size evolution in ferns

Recent studies investigating the evolution of genome size diversity in ferns have shown that they have a distinctive genome profile compared with other land plants. Ferns are typically characterized by possessing medium‐sized genomes, although a few lineages have evolved very large genomes. Ferns are different from other vascular plant lineages as they are the only group to show evidence for a correlation between genome size and chromosome number. In this study, we aim to explore whether the evolution of fern genome sizes is not only shaped by chromosome number changes arising from polyploidy but also by constraints on the average amount of DNA per chromosome. We selected the genus Asplenium L. as a model genus to study the question because of the unique combination of a highly conserved base chromosome number and a high frequency of polyploidy. New genome size data for Asplenium taxa were combined with existing data and analyzed within a phylogenetic framework. Genome size varied substantially between diploid species, resulting in overlapping genome sizes among diploid and tetraploid spleenworts. The observed additive pattern indicates the absence of genome downsizing following polyploidy. The genome size of diploids varied non‐randomly and we found evidence for clade‐specific trends towards larger or smaller genomes. The 578‐fold range of fern genome sizes have arisen not only from repeated cycles of polyploidy but also through clade‐specific constraints governing accumulation and/or elimination of DNA.